Today’s birds may have inherited their distinctive crouching posture from ancestors whose hind limbs had to compensate for the weight of increasingly beefy forelimbs, aka wings. New findings, though preliminary, suggest that changes both fore and aft may have been important in the evolution of flight.

Members of the dinosaur lineage that led to modern birds stood upright, with stubby, clawed forelimbs suited to tearing at flesh. But over millions of years, the bodies of creatures on the bir...